1. Field of the Invention
The present invention relates to an electrophotographic apparatus and a process cartridge.
2. Description of the Related Art
In recent years, the following apparatuses have been widely used: electrophotographic apparatuses using a contact charging method in which a voltage is applied to a charging member (contact charging member) contacting a cylindrical electrophotographic photosensitive member such that the electrophotographic photosensitive member is charged. Examples of the contact charging method include an AC/DC contact charging method in which a voltage obtained by superimposing an alternating-current voltage on a direct-current voltage is applied to the charging member and a DC contact charging method in which a direct-current voltage only is applied to the charging member.
In the contact charging method, the influence of discharge occurring near a contact surface of the charging member strongly acts on the electrophotographic photosensitive member and therefore a surface of the electrophotographic photosensitive member is likely to be worn. Japanese Patent Laid-Open No. 2005-300741 describes that the local surface abrasion of an electrophotographic photosensitive member is reduced by adjusting the distance between the position of an end portion of a charging unit and the position of an end portion of a development unit to 8 mm or less.
Japanese Patent Laid-Open No. 01-277269 discloses an electrophotographic apparatus having an effective transfer width less than an effective charge width and describes that the contamination of a transfer unit with tonner is reduced.
Japanese Patent Laid-Open No. 2005-172863 describes that a surface layer of an electrophotographic photosensitive member contains a compound cured by polymerization and a contact charging member and a cleaning member are brought into contact with each other in a region where the surface layer is present. This reduces the local surface abrasion of the electrophotographic photosensitive member that contacts an end portion of the contact charging member.
Recently, electrophotographic apparatuses have been required to increase the rotation speed of an electrophotographic photosensitive member in association with an increase in print speed and have been required to efficiently clean spherical or small-particle toner used to achieve high image quality. This increases the friction of a charging unit with the electrophotographic photosensitive member. Investigations performed by the inventors have revealed that the local surface abrasion of the electrophotographic photosensitive member needs to be improved in an end portion of a contact region between the electrophotographic photosensitive member and the charging unit. In particular, the discharge current flowing through the end portion of the contact region between the electrophotographic photosensitive member and the charging unit is larger than the discharge current flowing through a central portion of the contact region therebetween and therefore the current density of the end portion is specifically high. This probably causes the chemical deterioration of a surface of the electrophotographic photosensitive member, which is likely to be worn by the friction with the charging unit. The local surface abrasion of the electrophotographic photosensitive member is likely to induce the leakage of a charging bias to cause image defects.